Process for making PEN/PET blends and transparent articles therefrom

ABSTRACT

Process for controlling the rate of change of intrinsic viscosity and transesterification during solid stating of a polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) blend, with an effective amount of an ethylene glycol compound. The process enables the production of a copolymer based on predefined initial and final IV&#39;s and final transesterification level, by varying the solid-stating time and/or effective amount of ethylene glycol. In one embodiment, a relatively greater amount of post-consumer PET (e.g., 70%) having an IV of on the order of 0.72-0.73, is incorporated in the blend to provide a final IV on the order of 0.80-0.85, and a moderate, controlled level of transesterification; the blend is used to injection mold a sleeve layer of a preform. In another embodiment, a substantially transparent neck finish for a preform is made from a PEN/PET blend having an amount of ethylene glycol which enables substantial transesterification, without excessive increase in IV.

FIELD OF THE INVENTION

The present invention concerns a process for making polyethylenenaphthalate and polyethylene terephthalate blends, and more particularlyto a method of controlling the rate of change of intrinsic viscosity andlevel of transesterification during solid stating of such blends.

BACKGROUND OF THE INVENTION

Polyethylene naphthalate (PEN) has a significantly higher glasstransition temperature (T_(g)) than polyethylene terephthalate (PET),i.e., about 120° C. compared to 80° C., as well as a five timeimprovement in oxygen barrier property. PEN is thus a desirable polymerfor use in thermal-resistant beverage containers (e.g., hot-fillable,refillable and/or pasteurizable containers), and for packagingoxygen-sensitive products (e.g., beer, juice). However, PEN is moreexpensive (both as a material and in processing costs) than PET and,therefore, the improvement in properties must be balanced against theincreased expense.

One method of achieving an article that is lower in cost than PEN, butwith higher thermal and barrier properties, is to provide a blend of PENand PET. However, blending of these two polymers often results in anopaque material with incompatible phases. Efforts to produce a clearcontainer or film from a PEN/PET blend have been ongoing for over tenyears, but there is still no commercial process in widespread use forproducing such articles.

One suggested method for making substantially transparent PEN/PET blendsis a solid-stating process which increases the level oftransesterification (copolymerization) between the two polymers. Forexample, WO 92/02584 (Eastman) states that transesterification occurswhen the melt blended, crystallized polymer is held at a temperaturebelow the melting point and subjected to an inert gas flow in order toraise the inherent viscosity and/or remove acetaldehyde. Thistransesterification is in addition to that occurring during meltblending and molding operations. However, Eastman reports that when thelevel of transesterification between the two polymers is very high, thecrystallinity and resultant physical properties of the blend are reducedto the point where they are undesirable for making oriented containerswith good mechanical properties.

Eastman teaches the addition of a phosphorus stabilizer for controlling(reducing) the amount of transesterification which occurs during solidstating. In this way, Eastman claims to limit the amount oftransesterification to an amount no greater than about 20%, based on atheoretical maximum amount of transesterification being equal to 100%.For example, in Table 2 Eastman describes the transesterification andinherent viscosity of various solid-stated PEN/PET blends, where theinitial inherent viscosity of the blend was on the order of 0.55 to0.65, and the final inherent viscosity was about 0.80 to 0.85. In acontrol example (50--50 PEN/PET) the final inherent viscosity wasacceptable (0.86) after eight hours, but the percent transesterification(25.0) was too high (above 20%). By adding 0.5 or 1.0% Ultranox 626 (aphosphite stabilizer) in the first two examples, the Eastman processprovided a final inherent viscosity of 0.80 to 0.84 after eight hours,and an acceptable percent transesterification of 17.0 or 19.0 (below20%). The other three stabilizers/metal deactivators tested in Table 2failed to provide the final desired inherent viscosity andtransesterification levels.

Although the Eastman process may be suitable for certain limitedstarting materials and desired transesterification levels, it cannot beexpanded generally to different combinations of intrinsic viscosity,solid-stating time, and levels of transesterification. For example, ofpotential interest is a blend made from precursor homopolymer PEN andpost-consumer PET (PC-PET). The intrinsic viscosity of PC-PET is muchhigher than that of virgin fibre-grade PET, so that a blend ofPEN/PC-PET would require a relatively larger amount oftransesterification per unit intrinsic viscosity increase (compared to ablend of PEN/virgin PET). Hence, among other disadvantages, the priorart does not provide a process that allows a desired level of bothintrinsic viscosity and transesterification level.

It is possible to make substantially transparent preforms (for blowmolding into containers) with a PET/PEN blend, without solid stating,but the disadvantages are such that the process is not commerciallyviable. First, the preform injection molding temperature (i.e., barreltemperature) and/or the equilibration time (i.e., time in the barrel)must be increased such that the resulting process is not cost-efficientor sufficiently reproducible for a commercial process. For example, incertain cases, the barrel time would be increased by a factor of four(i.e., an increase over the standard cycle of 45 seconds of up to 180seconds); as a result, one would probably not be able to run the processon a standard injection molding machine. Furthermore, the increase inbarrel time/temperature increases the acetaldehyde (AA) levels in thepreform to an unacceptably high level, such that AA is likely to beextracted into the food product and produce an off taste, particularlywith a product such as bottled water. Thus, this has not proven to bethe desired solution.

SUMMARY OF THE INVENTION

According to the present invention, a process is provided forcontrolling both the rate of change of intrinsic viscosity (IV) and therate of transesterification of a blend of polyethylene terephthalate(PET) and polyethylene naphthalate (PEN) during solid stating. Themethod comprises providing PEN having a first intrinsic viscosity (IV),providing PET having a second IV, and reacting the PEN and PET in thepresence of an ethylene glycol compound in an amount sufficient toachieve a desired final IV and final level of transesterification in thecopolymerized PEN/PET product.

In one embodiment, a full-length preform sleeve layer is made from aPEN/PET blend having an effective amount of ethylene glycol to increasethe T_(g) at least about 15° C. Other layers of the preform body may bePET. In this embodiment, a moderate, controlled level oftransesterification is provided to enable strainorientation/crystallization in both the blend and PET layers foroptimizing the mechanical performance, while maintaining optical clarity(substantial transparency).

In another embodiment, the process is used for making container preformshaving a neck finish with a transesterification level of at least about30% or greater. For example, a 30% PEN and 70% PET weight percent blendincludes an effective amount of ethylene glycol to obtain a desired highlevel of transesterification, but without raising the molecular weight(i.e., intrinsic viscosity) too high. This blend will provide a highT_(g) neck finish portion and is also melt compatible with adjacent PETlayers to maintain clarity and adhesion. Because the neck finish is notstretched, there is no need to provide a lower level oftransesterification as would be required to enable strainorientation/crystallization.

In other embodiments, the method of this invention enables the use ofinitial higher molecular weight polymers. For example, it may bedesirable to utilize post-consumer PET (PC-PET), having an initial IV of0.72-0.73 dL/g, in an amount of from about 60-90 weight percent, withthe remaining component being PEN. A predetermined final IV andtransesterification level are achieved by adjusting the solid statingtime and/or amount of ethylene glycol used.

These and other features and advantages of the present invention aremore particularly described with regard to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF FIGURES

FIGS. 1-2 are graphs showing the change in melting temperature (MP) andorientation temperature (T_(g)) for various PEN/PET random copolymercompositions;

FIG. 3 is a cross-sectional view of a preform embodiment of the presentinvention having a full-length inner body sleeve of the PEN/PET blend;

FIG. 4A is a front elevational view of a returnable and refillablecarbonated beverage container, partially in section, made from thepreform of FIG. 3, and FIG. 4B is an enlarged fragmentary cross-sectionof the container sidewall taken along the line 4B--4B of FIG. 4A;

FIG. 5A is a cross-sectional view of another preform embodiment of thepresent invention having a monolayer neck finish insert and a multilayerbody portion, and FIG. 5B is an enlarged fragementary cross section viewof the neck finish/body junction of the preform of FIG. 5A;

FIG. 6 is a graph of intrinsic viscosity versus solid-stating timeillustrating the rate of IV increase for various compositions;

FIG. 7 is a graph of the percent transesterification versussolid-stating time illustrating the rate of transesterification forvarious compositions;

FIG. 8 is a graph of the initial drop in intrinsic viscosity as afunction of the weight percentage of ethylene glycol added to thereaction mixture prior to solid stating;

FIG. 9 is a graph of the rate of intrinsic viscosity gain versus theweight percentage of ethylene glycol added to the reaction mixture priorto solid stating; and

FIG. 10 is a graph of the rate of transesterification as a function ofthe weight percentage of ethylene glycol added to the reaction mixtureprior to solid stating.

DETAILED DESCRIPTION

When PET/PEN blends are subjected to a solid-stating process, forexample to increase the IV and/or to reduce acetyldehyde generation, theamount or level of transesterification is increased, based on atheoretical maximum amount of transesterification (randomcopolymerization) of 100%. Transesterification is measured by nuclearmagnetic resonance spectroscopy (NMR)--more specifically by determiningthe relative area in the NMR curves of the ethylene protons associatedwith naphthalenedicarboxylate-ethylene glycol-terephthalate units,compared to what would be found for a completely random copolymer madewith naphthalenedicarboxylic acid, terephthalic acid, and ethyleneglycol. The random copolymer would be considered to have 100%transesterification.

The PEN/PET blend may be formed by extrusion compounding, pelletizing,crystallizing and then solid stating to a desired transesterificationlevel. Subsequently, it is contemplated that the solid-stated polymerwill be extruded or injection molded to form a preform; this step islikely to produce a reduction in IV and increase in transesterification.Finally, the preform will be expanded (e.g., blow molded) into asubstantially transparent container or other article.

There are three significant variables in the solid-stating process,namely the change in IV, the solid-stating time, and the change intransesterification level. Temperature is also important but is usuallyset to the highest temperature possible without melting the polymerblend. Generally, for a given application, the initial and final IV arespecified, as well as the final level of transesterification. It wouldbe desirable to control the process to achieve these predeterminedparameters, by adjusting the solid-stating time and/or by the use ofadditives. According to the present invention, the amount of ethyleneglycol present during the solid-stating process can be used to controlboth the rate of change of IV and the rate of transesterification. Inparticular, it has been found that adding an increasing amount ofethylene glycol to the blend prior to solid stating results in acopolymer having a higher level of transesterification. This result issurprising since conventional wisdom indicates that adding ethyleneglycol to the reaction mixture would result in a decrease in the levelof transesterification of the resulting copolymer.

More particularly, it is desirable to add PEN to a PET polymer in orderto increase the thermal performance, i.e., T_(g). However, at PEN levelson the order of 20-80 weight percent in a random copolymer (see FIGS.1-2), the blend is substantially amorphous, which means the materialcannot be crystallized. Generally, a crystallizable material is requiredin a stretch blow-molded article because it provides the necessarylevels of orientation and barrier properties, and controls the materialdistribution. Also, with PET/PEN blends, there is a problem withincompatible phases rendering the article opaque.

Generally, too low a level of transesterification provides a PEN/PETpreform of poor clarity (i.e., not substantially transparent), while toohigh a level of transesterification prevents crystallinity (i.e.,strain-induced crystallization and the resulting improved mechanicalproperties). Thus, in certain applications there is some intermediatelevel of transesterification desired in order to obtain both substantialtransparency and good mechanical properties. The specific level oftransesterification required will vary with the relative amounts of thepolymers, their IV's, layer thicknesses, use temperature, use ofcopolymers, etc.

In other applications, the PEN/PET blend may have a relatively highlevel of transesterification. The copolymers of the present inventionhaving a transesterification of greater than about 30% demonstrateproperties similar to copolymers having a transesterification level ofabout 100% (i.e., truly random copolymers). Thus, a relatively highlevel of transesterification as used herein refers to a copolymer havinga transesterification level of greater than about 30%, and morepreferably greater than about 35%. As known to those skilled in the art,the actual level of transesterification at which a copolymerdemonstrates the properties of a truly random copolymer depends on avariety of parameters.

FIGS. 1-2 illustrate graphically the change in melt temperature (MP) andorientation temperature (T_(g)) for PET/PEN near random copolymercompositions, as the weight percent of PEN increases from 0 to 100.There are three classes of PET/PEN compositions: (a) a high-PENconcentration having on the order of 80-100% PEN and 0-20% PET by totalweight of the composition, which is a strain-hardenable (orientable) andcrystallizable material; (b) a mid-PEN concentration having on the orderof 20-80% PEN and 80-20% PET, which is an amorphous non-crystallizablematerial that, when at a relatively high level of transesterification,will not undergo strain hardening; and (c) a low-PEN concentrationhaving on the order of 1-20% PEN and 80-99% PET, which is acrystallizable and strain-hardenable material. A particular PEN/PETcomposition can be selected from FIGS. 1-2 based on the particularapplication.

The PEN and PET polymers useful in the blends of this invention arereadily prepared using typical polyester polycondensation reactionconditions known in the art. They can be made by either a batch orcontinuous process to a desired IV value. Examples of methods which maybe employed to prepare the PET and PEN polymers useful in the presentinvention are found in U.S. Pat. No. 4,617,373.

For example, polyethylene naphthalate (PEN) is a polyester produced whendimethyl 2,6-naphthalene dicarboxylate (NDC) is reacted with ethyleneglycol. The PEN polymer comprises repeating units of ethylene 2,6naphthalate. PEN resin is available having an inherent viscosity of 0.67dl/g and a molecular weight of about 20,000 from Eastman Chemical Co.,Kingsport, Tenn. PEN has a glass transition temperature T_(g) of about123° C., and a melting temperature MP of about 267° C.

Either or both of the PET and PEN polymers may optionally be modifiedwith various materials such as dicarboxylic acids, glycols,cyclohexanes, xylenes and bases appropriate for amide formation. Suchmodifying materials are typically precompounded with the PET or PEN.Thus, as used herein PET and PEN are meant to include such modifiedpolymers.

When dicarboxylic acids are used as the modifying materials, the PEN orPET should include up to 15 mol %, and preferably up to 10 mol %, of oneor more of the dicarboxylic acids (i.e., different thannaphthalenedicarboxylic acid isomer(s) in the case of PEN and differentthan terephthalic acid isomer(s) in the case of PET) containing 2 to 36carbon atoms, and/or one or more different glycols (i.e., different thanethylene glycol) containing 2 to 12 carbon atoms.

Typical modifying dicarboxylic acids for PEN include terephthalic,isophthalic, adipic, glutaric, azelaic, sebacic, fumaric andstilbenedicarboxylic acid and the like. Typical examples of a modifyingglycol for PEN include 1,4-butanediol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, and the like.The PEN polymers are preferably derived from 2,6-naphthalenedicarboxylicacid, but may be derived from 2,6-naphthalenedicarboxylic acid and alsocontain, optionally, up to about 25 mol % (preferably up to 15 mol %,more preferably up to 10 mol %) of one or more residues of differentnaphthalenedicarboxylic acid isomers such as the 1,2-, 1,3-, 1,4-, 1,5-,1,6-, 1,7-, 1,8-, 2,3-, 2,4-, 2,5-, 2,7- or 2,8-isomers. PEN polymersbased primarily on 1,4-, 1,5-, or 2,7-naphthalenedicarboxylic acid arealso useful.

Typical glycols used for modifying PEN include but are not limited toalkylene glycols, such as ethylene glycol, propylene glycol, butyleneglycol, pentylene glycol, 1,6-hexanediol, and2,2-dimethyl-1,3-propanediol.

Cyclohexane modifiers appropriate for use with PEN are nonaromatic6-member ring compounds which can act as base portions in condensationreactions. Such compounds include, for example, 1,4-cyclohexanedimethanol (CAS # 105-08-8, available from Aldrich Chemicals, Milwaukee,Wis., U.S.A).

Xylenes appropriate for modifying PEN are benzene-containing compoundswhich include at least one methyl group bonded to the benzene ring andwhich may have additional alkyl groups bonded to the benzene ring. Suchxylenes include, for example, toluene, xylene, methylethylbenzene,methylpropylbenzene and methylbutylbenzene.

PEN modifying amide-forming bases appropriate for use in the presentinvention include metaxylenediamine (CAS # 1477-055-0, available fromAldrich Chemicals), hexamethylenediamine (CAS # 124-09-4, available fromAldrich Chemicals), and the like.

Typical modifying dicarboxylic acids for PET include isophthalic acid,adipic acid, glutaric acid, azelaic acid, sebacic acid, fumaric acid,stilbenedicarboxylic acid, biphenyidicarboxylic acid, any of the isomersof naphthalenedicarboxylic acid, and the like. Typical modifying glycolsfor PET include alkylene glycols, such as ethylene glycol, propyleneglycol, butylene glycol, pentylene glycol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, and the like. The aforementionedcyclohexanes, xylenes and amides may also be used to modify PET.

Commercially available "bottle grade" PET includes PET homopolymer andPET copolymers suitable for making containers, which are well-known inthe art. These PET copolymers may include a minor proportion, forexample up to about 10% by weight, of monomer units which are compatiblewith the ethylene terephthalate units. For example, the glycol moietymay be replaced by an aliphatic or alicylic glycol such as cyclohexanedimethanol (CHDM). The dicarboxylic acid moiety may be substituted by anaromatic dicarboxylic acid such as isophthalic acid (IPA).

Post-consumer PET (PC-PET) is a type of recycled PET prepared from PETplastic containers and other recyclables that are returned by consumersfor a recycling operation, and has now been approved by the FDA for usein certain food containers. PC-PET is known to have a certain level ofI.V. (intrinsic viscosity), moisture content, and contaminants. Forexample, typical PC-PET (having a flake size of one-half inch maximum),has an I.V. average of about 0.073 dl/g to about 0.74 dl/g, a moisturecontent of less than 0.25%, and the following levels of contaminants:

PVC: <100 ppm

aluminum: <50 ppm

olefin polymers (HDPE, LDPE, PP): <500 ppm

paper and labels: <250 ppm

colored PET: <2000 ppm

other contaminants: <500 ppm

PC-PET may be used alone or in one or more layers for reducing the costor for other benefits.

The amount of PET in the blend (i.e., component (A)) is preferably offrom about 50 to about 90 weight %, and more preferably of from about 60to about 80 weight %. Accordingly, the amount of PEN in the blend (i.e.,component (B)) is preferably of from about 10 to about 50 weight %, andmore preferably of from about 20 to about 40 weight %.

An amount of ethylene glycol may be used effective to substantiallyreduce the rate of increase of intrinsic viscosity (molecular weight)during solid stating. The desired overall increase (or decrease) of IVand increase in transesterification can be selected by varying theamount of glycol weight percent, depending upon the particular initialand final IV, transesterification level, and solid-stating time.Typically, the effective amount of ethylene glycol would be at leastabout 0.05 weight percent, based on the weight of the polymer blend,preferably from about 0.1 to 2%, and more preferably from about 0.1% to0.5%. Ethylene glycol, CH₂ OHCH₂ OH, is a clear, colorless liquid havinga specific gravity of 1.1155 (20° C.) and a boiling point of 197.2° C.

The solid-stating procedure which results in transesterification of thePET/PEN blends can be any solid-stating procedure commonly used in thepolyester art to increase IV and/or reduce the acetaldehydeconcentration. Basically, solid stating is a procedure wherein a solidpolymer is heated until the desired level of IV build-up is achieved anda means for removing glycol during heating is provided. However,according to the present invention, the amount of ethylene glycolpresent is manipulated such that the desired final IV andtransesterification level are achieved.

The amount of heating is between the highest glass transitiontemperature (T_(g)) of the polymers present and the lowest meltingtemperature (MP) of the polymers present. Typically, the temperatureduring solid stating is between about 150° C. and about 250° C.,preferably between about 210° C. and 250° C., and more preferablybetween about 215° C. and about 230° C. The amount of IV build-up fortypical solid-stating process is an increase of at least about 5%, andpreferably at least about 10%. Usually, no more than a 50% increase inIV is desired, although higher build-up is commercially useful for someapplications (e.g., tire cord).

The time required for solid stating will vary; at least about 6 hours,and up to about 30 hours, is typical. Preferably, no more than about 24hours is desired.

Nitrogen flow or vacuum used during the solid-stating process must bestrong enough to remove ethylene glycol from the reaction mixture suchthat the amount of ethylene glycol present in the reaction mixtureresults in the desired final IV and transesterification level. There aretwo sources of this ethylene glycol. The first source is the ethyleneglycol that is added to the reaction mixture prior to the reaction, andthe second source is the ethylene glycol formed as a by-product of thecondensation reaction of functional end groups of the polymer chains. Ithas been found that by adding a specified amount of liquid ethyleneglycol prior to the solid stating process, while drawing off ethyleneglycol during the reaction, that the IV and transesterification ratescan be controlled.

As is readily apparent to a skilled artisan, all parameters for solidstating (such as time, temperature and chemical nature of polymer(s))are interdependent and will be varied to accommodate a particulardesired result.

The compositions of the present invention are suited forhigh-temperature packaging applications such as hot-fillable, returnableand refillable, and pasteurizable food and beverage containers. Theparticular overall blend composition desired can be determined by thebarrier and thermal properties needed for the end use requirements.

The intrinsic viscosity (IV) affects the processability of the polyesterresin. Polyethylene terephthalate having an intrinsic viscosity of about0.8 is widely used in the carbonated soft drink industry. Resins forvarious applications may range from about 0.6 to about 1.2, and moreparticularly from about 0.65 to about 0.85. 0.6 correspondsapproximately to a viscosity average molecular weight of 59,000, and 1.2to a viscosity average molecular weight of 112,000.

Intrinsic viscosity measurements may be made according to the procedureof ASTM D-2857, by employing 0.0050±0.0002 g/ml of the polymer in asolvent comprising o-chlorophenol (melting point 0° C.), respectively,30° C. Intrinsic viscosity is given by the following formula:

    IV=(In(V.sub.Soln. /V.sub.Sol.))/C

where:

V_(Soln). is the viscosity of the solution in any units;

V_(Sol). is the viscosity of the solvent in the same units; and

C is the concentration in grams of polymer per 100 mls of solution.

The I.V.s of PEN and PET polymers before solid stating are typicallyabout 0.5 to about 0.8, and more typically about 0.6 to about 0.7. TheIV's of the polymers after solid stating are typically about 0.5 toabout 1.0, and more typically about 0.7 to about 0.8.

The preform and blown containers should be substantially transparent. Ameasure of transparency is the percent haze for transmitted lightthrough the wall (H_(T)) which is given by the following formula:

    H.sub.T = Y.sub.d ÷(Y.sub.d +Y.sub.s)!×100

where Y_(d) is the diffuse light transmitted by the specimen, and Y_(s)is the specular light transmitted by the specimen. The diffuse andspecular light transmission values are measured in accordance with ASTMmethod D1003, using any standard color difference meter such as modelD25D3P manufactured by Hunterlab, Inc. A substantially transparentcontainer should have a percent haze (through the wall) of less thanabout 15%, preferably less than about 10%, and more preferably less thanabout 5%.

A substantially amorphous preform should have a percent haze of no morethan about 20%, preferably no more than about 10%, and more preferablyno more than about 5%. The preform may be single layer or multilayer andmay be made in accordance with the well-known injection mold processes,such as described in U.S. Pat. No. 4,710,118 granted Dec. 1, 1987 toKrishnakumar et al., which is hereby incorporated by reference in itsentirety.

The materials, wall thicknesses, preform and bottle contours, may all bevaried for a specific end product while still incorporating thesubstance of this invention. The container may be for pressurized orunpressurized beverages, including beer, juice and milk, or fornon-beverage products.

The improved thermal resistance provided by this invention makes itparticularly suitable for hot-fill containers. Hot-fill containerstypically must withstand elevated temperatures on the order of 180-185°F. (the product filling temperature) and positive internal pressures onthe order of 2-5 psi (the filling line pressure) without substantialdeformation, i.e., a volume change of no greater than about ±1%. Otherfactors important in the manufacture of hot-fill containers aredescribed in U.S. Pat. No. 4,863,046 to Collette et al. granted Sep. 5,1989, which is hereby incorporated by reference in its entirety.

The enhanced thermal resistance of the PEN/PET blends of this inventionare also particularly useful as one or more layers of a refillablecarbonated beverage container able to withstand numerous refill cycleswhile maintaining aesthetic and functional features. A test procedurefor simulating such a cycle without crack failure and with a ±1.5%maximum volume change is as follows.

Each container is subjected to a typical commercial caustic washsolution prepared with 3.5% sodium hydroxide by weight and tap water.The wash solution is maintained at the desired wash temperature, e.g.,60° C., 65° C., etc. The bottles are submerged uncapped in the wash for15 minutes to simulate the time/temperature conditions of a commercialbottle wash system. After removal from the wash solution, the bottlesare rinsed in tap water and then filled with a carbonated water solutionat 4.0±0.2 atmospheres (to simulate the pressure of a carbonated softdrink container), capped and placed in a 38° C. convection oven at 50%relative humidity for 24 hours. This elevated oven temperature isselected to simulate longer commercial storage periods at lower ambienttemperatures. Upon removal from the oven, the containers are emptied andagain subjected to the same refill cycle, until failure.

A failure is defined as any crack propagating through the bottle wallwhich results in leakage and pressure loss. The volume change isdetermined by comparing the volume of liquid the container will hold atroom temperature, both before and after each refill cycle.

The container can preferably withstand at least 10 refill cycles, andpreferably 20 refill cycles at a wash temperature of at least 60° C.without failure, and with no more than about ±1.5% volume change intotal.

For use as a refillable bottle, the bottle preferably has a relativelythick champagne base made in accordance with the prior art refillcontainers described in Continental PET Technologies, Inc.'s U.S. Pat.Nos. 4,725,464 and 5,066,528, which are hereby incorporated by referencein their entirety. The dome and chime form a thickened base portionhaving about 3-4 times the thickness of the cylindrical sidewall, andhaving an average crystallinity of no greater than about 10%. Radiallyoutwardly of the chime, there is a thinner outer base portion of about50-70% of the thickness of the thickened base portion and increasing incrystallinity up to its junction with the sidewall. The thinner outerbase wall provides improved impact resistance. The thickened dome andchime provide improved resistance to caustic cracking.

A preferred planar stretch ratio is 8-12:1 for a cylindrical sidewall ofa polyester refill beverage bottle of about 0.5 to 2.0 liters/volume,and more preferably about 9-11:1. The hoop stretch is preferably 3-3.6:1and the axial stretch 2.4-3:0. This produces a container sidewall withthe desired abuse resistance, and a preform sidewall with the desiredvisual transparency. The sidewall thickness and stretch ratio selecteddepend on the dimensions of the specific bottle, the internal pressure(e.g., 2 atm for beer, 4 atm for soft drinks) and the processingcharacteristics of the particular material (as determined for example,by the intrinsic viscosity).

The cylindrical sidewall portion of the container which is blown to thegreatest extent has the highest average percent crystallinity,preferably about 25-35%. The tapered shoulder, which is also expandedsubstantially more than the base, preferably has an average percentcrystallinity of 20-30%. In contrast, the substantially thickened andlesser blown base has a crystallinity of about 0-10% in the dome andchime, and increases in crystallinity in the outer base moving upwardlytowards the sidewall. The neck finish is not expanded and remainssubstantially amorphous at 0-2% crystallinity.

Various levels of crystallinity can be achieved by a combination ofexpansion (strain-induced) and heat-setting (thermal-induced).

Methods of making a full-length sleeve and/or separate neck finishportion according to the examples shown in FIGS. 3-6 are described incopending and commonly owned U.S. Ser. No. 08/534,126 filed Sep. 26,1995, entitled "PREFORM AND CONTAINER WITH CRYSTALLIZED NECK FINISH ANDMETHOD OF MAKING THE SAME," by Wayne N. Collette and Suppayan M.Krishnakumar, which in turn is a continuation-in-part of copending andcommonly owned U.S. Ser. No. 08/499,570 filed Jul. 7, 1995, entitled"APPARATUS AND METHOD FOR MAKING MULTILAYER PREFORMS," by Suppayan M.Krishnakumar and Wayne N. Collette, both of which are herebyincorporated by reference in their entirety.

FIG. 3 shows a preform 30 which includes an outer layer 22 and afull-length inner sleeve layer 20, the sleeve having a portion 21extending over the top sealing surface of the neck finish.

FIGS. 4A-4B illustrate a refillable carbonated beverage container, whichhas been stretch blow molded from the preform of FIG. 3. The multilayercontainer 40 includes in cross-section a biaxially-expanded inner layer41 formed from the preform inner sleeve layer 20, and biaxially-expandedouter layer 43 (formed from preform outer layer 22). The containerincludes an upper neck finish 42 (same as in the preform), a dome-shapedshoulder section 44, a cylindrical panel section 45, and a base 48. Thebase includes a recessed central dome 52, surrounding a central gate 51,a standing ring or chime 54 surrounding the dome, and an outermost baseregion 56 connecting the chime to the sidewall. FIG. 4B is an expandedview of the multilayer panel section 45, showing a relatively thin innerlayer 41 and relatively thicker outer layer 43. The PEN/PET blend of thepresent invention may be used as either the inner or outer layers, withthe other layer being PET or another compatible polymer. As a costsavings to minimize the use of PEN, the inner layer 41 may be thePEN/PET blend.

FIGS. 5A-5B illustrate another preform embodiment. In this case, amonolayer neck finish is made of the PEN/PET blend, to provide thermalresistance. This is particularly useful in hot-fillable containers. Amultilayer body portion may include one or more layers of PET, PC/PET, aPET/PEN blend of the present invention, or other compatible polymers.The container 330 includes a neck finish portion 340 and body portion350. The neck finish includes an open upper end 342 including a topsealing surface 341, external threads 343, and a lowermost flange 344.The body portion 350 includes an upper tapered portion 351, which willform the shoulder portion of the container, a cylindrical body portion352, which will form the panel of the container, and a lowerbase-forming portion 353. In this example, the body portion includesouter layer 354, core layer 356, and inner layer 358. In the centralbase portion there is a further layer 359 which is generally made toclear the nozzle of the core material, in preparation for the nextinjection molding cycle.

The following examples illustrate the invention, but should not beinterpreted as a limitation thereon.

EXAMPLE 1. PET/PEN

33.7 lbs of clean post-consumer PET flake, with an average IV of 0.74,and 16.3 lbs of pellets of a homopolymer PEN, with an IV of 0.67, arehand blended and dried at 300° F. using a D-100 desiccant dryer fromConair for a period of 8-10 hours at a dew point of -40° F. or lower.The 50-lb dried blend is then compounded on a 11/2" extruder with a 36:1L/D ratio and a compression ratio of 3:1. The entire transition zone isof a barrier design with a 0.010" clearance between the screw andbarrel. The output of the extruder is directed into a stranding dye;molten strands are then pulled through a water bath for cooling, and arefinally chopped into 1/4" long by 1/8" diameter pellets with a final IVof 0.68.

These pellets are then dried in vacuum with agitation at 250° F. for 3hours; they are then crystallized under vacuum with agitation at 350° F.for an additional hour before solid stating at 430° F. under high vacuumand agitation for a period of 24 hours in a Ross, Hauppauge, N.Y.,VB-001 Double Planetary Mixer. Processing of these materials under theseconditions yielded a transesterification level of 20%. The 24 hours ofsolid stating at an IV rate increase of 0.012/hr yielded pellets with anunacceptably high IV of 0.97. Although the 20% transesterification ratetargeted in this example was achieved, and the time of solid stateprocessing was reasonable, the final IV was too high to be used forcommercial production of stretch-blow molded bottles.

EXAMPLE 2. PET/PEN with 1% Ultranox 626

The same compounding steps as in Example 1 were conducted, but to the50-lb dried blend was added 1% (by weight) Ultranox 626 (Eastman'sphosphite stabilizer) and blended by hand. The pellet IV was 0.69.

The pellets were then dried, crystallized and solid stated as in Example1, but the solid-stating time was 36 hours. The transesterification ratewas 0.29/hour, and final transesterification level 10.5%. The 36 hoursof solid stating at an IV rate increase of 0.021/hr, yielded pelletswith an unacceptably high IV of well over 1.1. Thus, not only was thetransesterification level below target, but the IV was too high toproduce bottles. Also, the 36 hours of processing time was somewhatexcessive and not generally suitable for a commercial process.

EXAMPLE 3. PET/PEN with 0.5% Ethylene Glycol

The same compounding steps as in Example 1 were conducted but to the50-lb dried blend was added 0.5% (by weight) liquid ethylene glycol andmixed by hand in a bucket. The pellet IV was 0.50.

The pellets were dried, crystallized and solid stated as in Example 1,but the solid-stating time was 11 hours. The final transesterificationlevel was 20%. The 11 hours of solid stating at an IV rate increase of0.0056/hr yielded pellets with an IV of 0.55. Although a targeted 20%transesterification level was achieved, and the solid-stating time wasacceptable, the resultant IV was too low to be used for commercialproduction of stretch-blow molded bottles.

EXAMPLE 4. PET/PEN with 0.13% Ethylene Glycol

The same compounding steps as in Example 1 were conducted but to the50-lb dried blend was added 0.13% (by weight) liquid ethylene glycol.The pellet IV was 0.54.

The pellets were dried, crystallized and solid stated as in Example 1,but the solid stating time was 21 hours. The final transesterificationlevel was 20%. The 21 hours of solid stating at an IV rate increase of0.010/hr yielded pellets with an IV of 0.76. A targeted 20%transesterification level was achieved, the 0.76 IV was acceptable, andthe solid-stating time was acceptable for commercial production ofstretch-blow molded bottles. This example shows how adjusting the amountof ethylene glycol and solid-stating time provided the desired final IVand transesterification level.

EXAMPLE 5. Preform With PEN/PET Neck Finish

A preform utilizing a PEN/PET blend for the neck finish as shown inFIGS. 5A-5B was produced as follows.

35 pounds of virgin PET pellets, with an average IV of 0.80, and 15pounds of homopolymer PEN pellets, with an average IV of 0.60, were handblended and dried as in Example 1. In a polyethylene bucket, 0.3%ethylene glycol was added to the blend by hand. The mixture wascompounded as in Example 1. The pellet IV was 0.59.

The pellets were dried, crystallized and solid stated as in Example 1,but the solid-stating time was 26 hours. The final transesterificationlevel was 35%; the IV rate increase was 0.0082/hr to provide a final IVof 0.80.

The state of the material as it came out of the reactor was highlycrystalline, which allows for standard, PET drying and processingmethods to be used. However, when this material is later melted (duringinjection molding to form a preform), it does not recrystallize, but,rather, remains amorphous. The material's relatively high T_(g) of 92°C. allows it to withstand hot filling and pasteurizing temperatures whenincorporated into a preform neck finish. The comparatively hightransesterification level provides a material which is melt compatibleand generally adhering to adjacent layers of PET (i.e., resistingdelamination under normal use conditions).

The preform neck finish (as in FIG. 5A) may be produced on one injectionmolding machine, removed and placed within a second injection moldingmachine where the body portion is overmolded. Alternatively, both thebody and the finish of the preform can be made by different processingsteps within the same injection molding machine. The relatively highlevel of transesterification in the neck finish of this example isacceptable because it is not required to undergo strain orientedcrystallization.

The processing effects caused by adding ethylene glycol prior to solidstating according to the present invention, which distinguish thesolid-stating process of the present invention from the prior artsolid-stating processes, are further illustrated in FIGS. 6-11 and thefollowing table.

In the graph of FIG. 6, the Y axis is intrinsic viscosity (IV) asdetermined according to ASTM D/2857 (see prior discussion). On the Xaxis there is displayed the solid-stating time in hours, from 0 to 20hours. The compounding and solid-stating conditions were similar tothose described in the prior examples. As a reference (A)--see tablebelow--a composition of 100 weight % virgin PET 6307, available fromShell Company (Houston, Tex.), having an initial IV of 0.64 dL/g, wasused. After solid stating for about 16 hours, the final IV was 0.9, atan IV rate increase of 0.0163 (dL/g)/hour. As a control sample (B), acomposition of 8 molar % dimethyl terephthalate, and 92 weight %dimethyl-2,6-naphthalenedicarboxylate (PEN 15967 available from EastmanChemical Company, Kingsport, Tenn.), having an initial IV of 0.6338dL/g, was used. After about 14 hours of solid stating, the final IV was0.7641, at an IV rate increase of 0.012 (dL/g)/hour.

A first sample (C) according to the invention is the same as the controlsample but included in addition 0.125 weight % ethylene glycol. It hadan initial IV of 0.5440; after about 17 hours of solid stating, thefinal IV was 0.7254 at an IV rate increase of 0.011/hour. A secondsample (D) according to the invention is the same as the control samplebut included in addition 0.5 weight % ethylene glycol. It had an initialIV of 0.4478; after about 16 hours of solid stating the final IV was0.5429 at an IV rate increase of 0.0056/hour. A third sample (E)according to the invention is the same as the control sample butincluded in addition 2 weight % ethylene glycol. It had an initial IV of0.3665; after about 15 hours of solid stating the final IV was 0.3151,at an IV rate decrease of -0.0036/hour. Note that the third sample (E)had an overall negative change (decrease) in IV, i.e., the polymerchains were breaking up at a faster rate than they were combining. Asindicated, each of the three samples (C, D, E) according to theinvention has a significantly lower IV rate increase than the controlsample (B).

As a further distinction, a sample (F) in accordance with the prior artEastman patent included 67.4 weight % PET and 32.6 weight % PEN, and inaddition 1 weight % of Ultranox 626 (the phosphate stabilizer); it hadan initial IV of 0.6400 and a final IV of 0.9845 after about 17 hours,for an IV increase rate of 0.021/hour. Again, this is a significantlyhigher IV rate increase than the three samples (C, D, E) of the presentinvention.

The percent transesterification for the above copolymers B-F wasmeasured as a function of the amount of ethylene glycol for varioussolid stating times (FIG. 7). In addition, the initial IV drop, rate ofIV gain, and rate of transesterification were also measured. Theseresults are summarized in Table 1 and shown in FIGS. 6-10.

    ______________________________________                                                Rate of         Per-   Per-   Percent                             Percent      Rate of                                                Trans-    Sam- cent   cent   Phos- Ethylene                                    Initial                                          IV    esterifi-    ple  PET    PEN    phite Glycol IV    Change                                                cation    ______________________________________    A    100    0      0     0      0.6400                                          0.0163                                                --    B    67.4   32.6   0     0      0.6145                                          0.012 0.67    C    67.4   32.6   0     0.125  0.5440                                          0.011 0.86    D    67.4   32.6   0     0.5    0.4478                                          0.0056                                                1.78    E    67.4   32.6   0     2      0.3365                                          -0.0036                                                3.56    F    67.4   32.6   1     0      0.6338                                          0.021 0.25    ______________________________________

As is clear from Table I if no ethylene glycol is added to the reactionmixture, the rate of transesterification is relatively low. However, byadding an appropriate amount of ethylene glycol to the reaction mixture,the rate of transesterification is increased dramatically. Inparticular, by adding 2 weight percent of ethylene glycol to thereaction mixture, the rate of transesterification increases by a factorof more than five relative to a reaction mixture to which no ethyleneglycol was added prior to reaction. Thus, adding ethylene glycol to thereaction mixture prior to solid stating allows control of the IV andlevel of transesterification of the copolymer as well as thesolid-stating time.

FIG. 6 demonstrates that the intrinsic viscosity of the copolymerdecreases as the amount of ethylene glycol added to the reaction mixtureprior to solid stating is increased. Thus, by adding ethylene glycol,the molecular weight of the copolymer is reduced.

FIG. 7 shows that the percent transesterification increases as theamount of ethylene glycol added to the reaction mixture prior to solidstating is increased. This is an unexpected result since theconventional wisdom indicates that adding ethylene glycol should reducethe level of transesterification of the copolymer.

FIG. 8 shows that the initial IV drop in the copolymer increases as theweight percentage of ethylene glycol added to the reaction mixture priorto solid stating is increased. Hence, the added ethylene glycolincreases the rate at which the molecular weight of the copolymerdecreases.

FIG. 9 shows that the rate of IV gain during solid stating is reduced asthe weight percentage of ethylene glycol added to the reaction mixtureprior to solid stating is increased. As a result, the added ethyleneglycol decreases the rate at which the molecular weight increases.

FIG. 10 shows that the rate of transesterification increases as theweight percentage of ethylene glycol added to the reaction mixture priorto solid stating is increased. The result is surprising since theconventional wisdom dictates that the presence of this additionalethylene glycol should reduce the rate of transesterification of thecopolymer.

Although several preferred embodiments of this invention have beenspecifically illustrated and described herein, it is to be understoodthat variations may be made to the method of this invention withoutparting from the spirit and scope of the invention as defined in theappended claims.

We claim:
 1. A method of copolymerizing polyethylene naphthalate (PEN)and polyethylene terephthalate (PET) comprising:providing PEN having afirst intrinsic viscosity (IV); providing PET having a second IV;reacting the PEN and PET in the presence of ethylene glycol to form acopolymerized PEN/PET product, wherein the level of the ethylene glycolpresent during the reacting step is manipulated so that said ethyleneglycol is present in an amount selected to be effective to reduce therate of IV increase during the reacting step at least about 10% and tocontrol the transesterification rate to achieve a desired final IV andfinal level of transesterification in the copolymerized PEN/PET product.2. The method of claim 1, wherein the copolymerized PEN/PET productcomprises about 60 to 95 weight percent of PET and about 5 to 40 weightpercent of PEN.
 3. The method of claim 2, wherein the copolymerizedPEN/PET product comprises about 35 to 85 weight percent of PET and about15 to 35 weight percent of PEN.
 4. The method of claim 1, wherein thelevel of the ethylene glycol is at least about 0.05 weight percent basedon the total weight of the PEN and PET.
 5. The method of claim 1,wherein the level of the ethylene glycol is about 0.05 to 2 weightpercent based on the total weight of the PEN and PET.
 6. The method ofclaim 1, wherein either or both of the PET and PEN is modified with upto about 15 mol percent of one or more different dicarboxylic acidscontaining from 2 to 36 carbon atoms, one or more different glycolscontaining from 2 to 12 carbon atoms, or a mixture of the one or moredifferent dicarboxylic acids and the one or more different glycols. 7.The method of claim 1, wherein the reacting step is carried out at atemperature of about 175° C. to 250° C. for at least about 6 hours suchthat a level of transesterification of the copolymerized PEN/PET productis increased at least about 5%.
 8. The method of claim 1, wherein thereacting step is carried out at a temperature of about 215° C. to 240°C. for about 8 to 12 hours such that the level of transesterification ofthe copolymerized PEN/PET product is increased about 5 to 25%.
 9. Themethod of claim 1, wherein the reacting step is carried out at atemperature of about 175° .C to 250° C.
 10. The method of claim 1,wherein either or both of the PET and PEN is modified by including acompound selected from the group consisting of dicarboxylic acids,alkylene glycols,, cyclohexanes, xylenes, amide-forming bases andmixtures thereof.
 11. The method of claim 1, wherein either or both ofthe PET and PEN is modified by including a compound selected from thegroup consisting of ethylene glycol, propylene glycol, butylene glycol,cyclohexadimethanol, toluene and mixtures thereof.
 12. The method ofclaim 1, wherein the second IV is about 0.70 dL/g to 0.75 dL/g.
 13. Themethod of claim 1, wherein the PET is post-consumer PET (PC-PET). 14.The method of claim 1, wherein the amount of the ethylene glycol causesthe final IV to be greater than the second IV.
 15. The method of claim1, wherein the amount of the ethylene glycol is no greater than about 2%by total weight of the PEN and PET.
 16. The method of claim 1, whereinthe amount of the ethylene glycol is selected to decrease the time ofthe reacting step.
 17. The method of claim 1, wherein a phosphiteantioxidant is present in the reacting step in an amount sufficient toreduce the rate of transesterification during the reacting step.
 18. Themethod of claim 1, wherein the copolymerized PEN/PET product has a levelof transesterification greater than about 30%.
 19. The method of claim1, wherein both the amount of ethylene glycol and time of the reactingstep are selected to achieve the final IV and final level oftransesterification.
 20. The method of claim 1, further comprising usingthe copolymerized PEN/PET product to injection mold a substantiallytransparent article.
 21. The method of claim 1, further comprising usingthe copolymerized PEN/PET product to injection mold a substantiallytransparent preform.
 22. The method of claim 1, further comprising usingthe copolymerized PEN/PET product to injection mold a substantiallytransparent portion of a preform.
 23. The method of claim 1, furthercomprising using the copolymerized PEN/PET product to injection mold atleast one substantially transparent layer of a preform.
 24. The methodof claim 23, wherein the preform is molded with a substantiallytransparent PET layer adjacent to the at least one layer.
 25. The methodof claim 20, further comprising using the injection molded article toblow mold a substantially transparent expanded article.
 26. The methodof claim 25, wherein the expanded article is multilayer and includes atleast one first layer of the PEN/PET product and at least one secondlayer of polyester adjacent the first layer.
 27. The method of claim 20,wherein the article is a multilayer article.
 28. The method of claim 27,wherein the multilayer article includes at least one first layer of thePEN/PET product and at least one second layer of polyester adjacent thefirst layer.